Wing tip device

Abstract

A wing tip device for fixing to the outboard end of a wing, the wing defining a wing plane, includes: an upper wing-like element projecting upwardly with respect to the wing plane and having a trailing edge; and a lower wing-like element fixed with respect to the upper wing-like element and having a root chord and a trailing edge, the lower wing-like element root chord intersecting with the upper wing-like element, and the lower wing-like element projecting downwardly from the intersection. The upper wing-like element is larger than the lower wing-like element and the trailing edge of the lower wing-like element is adjacent the trailing edge of the upper wing-like element at the intersection. An included angle between the upper and lower wing-like elements at the intersection is less than, or equal to, 160 degrees.

Description

RELATED APPLICATIONS[0001]The present application is a National Phase of International Application Number PCT / EP2011 / 061552, filed Jul. 7, 2011, and claims priority from, British Application Number 1011843.8, filed Jul. 14, 2010.FIELD OF THE INVENTION[0002]The present invention relates to a wing tip device for fixing to the outboard end of a wing. Also, a wing with the wing tip device; an aircraft with the wing; a method of fitting, or retro-fitting, the wing tip device to a wing; a method of modifying an existing wing tip device; and a method of operating a wing with the wing tip device.BACKGROUND OF THE INVENTION[0003]A wing tip device is attached to the outboard end of a wing to reduce induced drag on the wing. In the case of e.g. an aircraft wing this can lead to improved fuel efficiency and reduced carbon emissions. Wing tip devices can take a variety of forms.[0004]A winglet is a wing-like element that extends from the wing tip. A winglet may extend upwardly or downwardly from...

AI Technical Summary

Benefits of technology

[0018]The invention is advantageous in that the lower wing-like element acts to offset at least some of the decrease in wing span that occurs due to aeroelastic deformation in the flight shape, whilst the upper and lower wing-like elements may still be optimised to meet any applicable span constraints in the ground shape. The addition of the lower element to a wing tip device comprising only an upper wing-like element (e.g. a winglet) has been shown to reduce drag on the wing / wing tip device combination by around a further 1.9% overall, with a vortex drag reduction of around a further 25 to 40% relative to that provided by the upper element alone.

[0032]In yet another embodiment, the upper wing-like element may include a substantially planar portion and a non-planar curved wing tip extension adapted to smoothly blend the outboard end of the wing into the substantially planar portion of the upper wing-like element. The upper element may be a winglet blended into the wing by a non-planar wing tip extension portion. The non-planar wing tip extension portion may have increasing curvature of local dihedral in the outboard direction. The wing tip extension portion helps to further reduce interference drag effects compared to a blended winglet with a constant radius transition.

Problems solved by technology

However, due to the bend induced on the wing shape from aeroelastic effects during flight, the wing span of the resulting flight shape is usually reduced and is therefore no longer optimal.

This traditional approach therefore carries a performance shortfall.

This problem becomes even more appreciable with greater use of relatively flexible wings to reduce structural weight, which tend to result in increased wing bending under aerodynamic load when compared to more rigid designs.

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